Many smoke detectors are known. The principle of an optical scattering-based smoke detector, for example, is based on utilizing, firstly, an emitter of light rays and, secondly, a receiver of light signals scattered by the ambient air. When there is no smoke in the air that enters the detector, the receiver only receives a very small amount of the scattered light. In contrast, when there is smoke in the air that enters the detector, this scatters the light from the emitter and thus lights the receiver.
To realize such smoke detectors, every emitter (typically a light-emitting diode) and receiver (typically a photodiode or phototransistor) component is positioned obliquely on a printed circuit, forming an angle of angle of approximately 35 to 45 degrees with this printed circuit.
However, the positioning of these components, which is very difficult to realize and test, is the main cause of manufacturing faults in the detectors and imposes high manufacturing costs. Faulty positioning can cause either a parasitic reflection blinding the receiver component or a reduction in sensitivity. In addition, the positioning of these components is not very reproducible, reducing the ability to establish a precise specification for the smoke detectors that comprise them. Lastly, the wires than connect these components to the printed circuit act as antennas collecting parasitic signals, thus reducing the detector's sensitivity.
In order to reduce these parasitic effects, document U.S. Pat. No. 5,138,302 proposes replacing the receiver by a component mounted directly on the printed circuit and collecting the light scattered by the smoke particles by using a lens positioned close to the receiver. However, in the proposed device the emitter comprises connecting wires to the printed circuit; this causes many drawbacks, for example, difficulty in correctly adjusting the angle between the emitted beams and the receiver's axis, the existence of an antenna effect towards the printed circuit likely to bring parasites to it, or the impossibility of properly defining the interaction zone. The problems mentioned above are therefore still to be resolved.
Ultimately, a significant portion of the circuit production is rejected before the detector is assembled, even when it is not the complete detector that is rejected during a test.
In addition, the problem of positioning the emitter and receiver components makes it difficult to utilize surface-mounted components (“SMC”) since they are miniaturized and therefore more sensitive to faulty positioning.
Document WO 2009/036988 is also known; it presents a radiation guide that can be surface-mounted, designed to be mounted on an emitter of light rays. However, the mechanical positioning of this radiation guide is still a problem and faulty positioning can lead to low sensitivity of the detector comprising two such radiation guides facing, respectively, an emitter and a receiver. The mechanical assembly of two guides requires the realization of a complex, therefore costly, part in which parasitic rays can go from the emitter to the receiver and hamper detection.